Cigarettes are tested by placing them in a holder and subjecting the oral end to a sub-ambient pressure after lighting the free end. The smoke resulting from this so-called "machine smoke" is passed through a disc shaped filter which is subsequently weighed and analyzed. Previous conventional holding devices for the cigarettes and the disc filters have comprised two conical, individually machined plastic parts which telescope together, the inner part having an outer circumferential groove to receive an O-ring seal which is pressed into the outer part to seal the chamber in which the filter disc is retained between the parts. The machined parts of these previous conventional holding devices are relatively heavy with respect to the filter disc and are made for repeated use. They have a tendency to absorb the products of combustion and thus become discolored. In addition, it has been recognized that the weight may change with use and the change in weight together with the discrepancy in relative weight between the filter and the holder has a tendency to reduce the accuracy of the test results.
U.S. Pat. No. 4,184,360, assigned to the assignee of the present invention, covers a cigarette testing filter assembly formed of light weight inexpensive plastic components. This has a number of advantages, one being that because of the light weight an accurate measurement of the amount of tars and nicotine collected can be made by weighing the entire assembly before and after the tests rather than requiring disassembly and assembly in order to weigh only the filter disc before and after the test. Another advantage is that because of the low cost, the entire assembly can be discarded after only one use thereby saving all the trouble and expense of cleaning between tests, as well as avoiding the testing inaccuracies which frequently result in repeated use despite the intermediate cleaning operations. But whereas the assembly covered by the aforesaid patent does have significant advantages, there are some problems with such an assembly one of which is that of attaining and retaining good seals between the components without requirement for maintaining close tolerances in the manufacture of the components. Also, just as is true of previous cigarette testing filter devices, it was found that at times there were erratic weight readings--weight readings not entirely accounted for by the actual amounts of tar and nicotine collected. It was recognized that with previous cigarette testing filter devices, erratic readings were generally due to small uncontrolled portions of the total amount of tars and nicotine from the cigarette being deposited not on the filter disc which was weighed but on other components which were not weighed. But until the discovery which led to one important aspect of the present invention, the reason for the sometimes erratic weight readings obtained with the assembly of the aforesaid patent remained a mystery.